Hide NullDimensionSelector from public (#6480)

extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/tuple/ArrayOfDoublesSketchAggregatorFactory.java

@@ -40,7 +40,6 @@ import org.apache.druid.segment.BaseObjectColumnValueSelector;
 import org.apache.druid.segment.ColumnSelectorFactory;
 import org.apache.druid.segment.ColumnValueSelector;
 import org.apache.druid.segment.DimensionSelector;
-import org.apache.druid.segment.DimensionSelectorUtils;
 import org.apache.druid.segment.NilColumnValueSelector;
 
 import javax.annotation.Nullable;
@@ -101,7 +100,7 @@ public class ArrayOfDoublesSketchAggregatorFactory extends AggregatorFactory
     // input is raw data (key and array of values), use build aggregator
     final DimensionSelector keySelector = metricFactory
         .makeDimensionSelector(new DefaultDimensionSpec(fieldName, fieldName));
-    if (DimensionSelectorUtils.isNilSelector(keySelector)) {
+    if (DimensionSelector.isNilSelector(keySelector)) {
       return new ArrayOfDoublesSketchNoOpAggregator(numberOfValues);
     }
     final List<BaseDoubleColumnValueSelector> valueSelectors = new ArrayList<>();
@@ -131,7 +130,7 @@ public class ArrayOfDoublesSketchAggregatorFactory extends AggregatorFactory
     // input is raw data (key and array of values), use build aggregator
     final DimensionSelector keySelector = metricFactory
         .makeDimensionSelector(new DefaultDimensionSpec(fieldName, fieldName));
-    if (DimensionSelectorUtils.isNilSelector(keySelector)) {
+    if (DimensionSelector.isNilSelector(keySelector)) {
       return new ArrayOfDoublesSketchNoOpBufferAggregator(numberOfValues);
     }
     final List<BaseDoubleColumnValueSelector> valueSelectors = new ArrayList<>();

processing/src/main/java/org/apache/druid/query/search/SearchQueryRunner.java

@@ -41,7 +41,6 @@ import org.apache.druid.segment.BaseFloatColumnValueSelector;
 import org.apache.druid.segment.BaseLongColumnValueSelector;
 import org.apache.druid.segment.ColumnValueSelector;
 import org.apache.druid.segment.DimensionSelector;
-import org.apache.druid.segment.DimensionSelectorUtils;
 import org.apache.druid.segment.Segment;
 import org.apache.druid.segment.column.ColumnCapabilities;
 import org.apache.druid.segment.column.ValueType;
@@ -127,7 +126,7 @@ public class SearchQueryRunner implements QueryRunner<Result<SearchResultValue>>
         final Object2IntRBTreeMap<SearchHit> set
     )
     {
-      if (!DimensionSelectorUtils.isNilSelector(selector)) {
+      if (!DimensionSelector.isNilSelector(selector)) {
         final IndexedInts row = selector.getRow();
         for (int i = 0, rowSize = row.size(); i < rowSize; ++i) {
           final String dimVal = selector.lookupName(row.get(i));

processing/src/main/java/org/apache/druid/segment/ConstantDimensionSelector.java

@@ -35,11 +35,11 @@ public class ConstantDimensionSelector implements SingleValueHistoricalDimension
 {
   private final String value;
 
-  public ConstantDimensionSelector(final String value)
+  ConstantDimensionSelector(final String value)
   {
     if (NullHandling.isNullOrEquivalent(value)) {
       // There's an optimized implementation for nulls that callers should use instead.
-      throw new IllegalArgumentException("Use NullDimensionSelector or DimensionSelectorUtils.constantSelector");
+      throw new IllegalArgumentException("Use DimensionSelector.constant(null)");
     }
 
     this.value = value;

processing/src/main/java/org/apache/druid/segment/DimensionSelector.java

@@ -20,11 +20,17 @@
 package org.apache.druid.segment;
 
 import com.google.common.base.Predicate;
+import org.apache.druid.common.config.NullHandling;
 import org.apache.druid.guice.annotations.PublicApi;
+import org.apache.druid.query.extraction.ExtractionFn;
 import org.apache.druid.query.filter.ValueMatcher;
 import org.apache.druid.query.monomorphicprocessing.CalledFromHotLoop;
 import org.apache.druid.query.monomorphicprocessing.HotLoopCallee;
+import org.apache.druid.query.monomorphicprocessing.RuntimeShapeInspector;
 import org.apache.druid.segment.data.IndexedInts;
+import org.apache.druid.segment.data.ZeroIndexedInts;
+import org.apache.druid.segment.filter.BooleanValueMatcher;
+import org.apache.druid.segment.historical.SingleValueHistoricalDimensionSelector;
 
 import javax.annotation.Nullable;
 import java.util.Arrays;
@@ -196,4 +202,138 @@ public interface DimensionSelector extends ColumnValueSelector<Object>, HotLoopC
       return Arrays.asList(strings);
     }
   }
+
+  static DimensionSelector constant(@Nullable final String value)
+  {
+    if (NullHandling.isNullOrEquivalent(value)) {
+      return NullDimensionSelectorHolder.NULL_DIMENSION_SELECTOR;
+    } else {
+      return new ConstantDimensionSelector(value);
+    }
+  }
+
+  static DimensionSelector constant(@Nullable final String value, @Nullable final ExtractionFn extractionFn)
+  {
+    if (extractionFn == null) {
+      return constant(value);
+    } else {
+      return constant(extractionFn.apply(value));
+    }
+  }
+
+  /**
+   * Checks if the given selector constantly returns null. This method could be used in the beginning of execution of
+   * some queries and making some aggregations for heuristic shortcuts.
+   */
+  static boolean isNilSelector(final DimensionSelector selector)
+  {
+    return selector.nameLookupPossibleInAdvance()
+           && selector.getValueCardinality() == 1
+           && selector.lookupName(0) == null;
+  }
+
+  /**
+   * This class not a public API. It is needed solely to make NULL_DIMENSION_SELECTOR and NullDimensionSelector private
+   * and inaccessible even from classes in the same package. It could be removed, when Druid is updated to at least Java
+   * 9, that supports private members in interfaces.
+   */
+  class NullDimensionSelectorHolder
+  {
+    private static final NullDimensionSelector NULL_DIMENSION_SELECTOR = new NullDimensionSelector();
+
+    /**
+     * This class is specially made a nested member of {@link DimensionSelector} interface, and accessible only through
+     * calling DimensionSelector.constant(null), so that it's impossible to mistakely use NullDimensionSelector in
+     * instanceof statements. {@link #isNilSelector} method should be used instead.
+     */
+    private static class NullDimensionSelector implements SingleValueHistoricalDimensionSelector, IdLookup
+    {
+      private NullDimensionSelector()
+      {
+        // Singleton.
+      }
+
+      @Override
+      public IndexedInts getRow()
+      {
+        return ZeroIndexedInts.instance();
+      }
+
+      @Override
+      public int getRowValue(int offset)
+      {
+        return 0;
+      }
+
+      @Override
+      public IndexedInts getRow(int offset)
+      {
+        return getRow();
+      }
+
+      @Override
+      public ValueMatcher makeValueMatcher(@Nullable String value)
+      {
+        return BooleanValueMatcher.of(value == null);
+      }
+
+      @Override
+      public ValueMatcher makeValueMatcher(Predicate<String> predicate)
+      {
+        return BooleanValueMatcher.of(predicate.apply(null));
+      }
+
+      @Override
+      public int getValueCardinality()
+      {
+        return 1;
+      }
+
+      @Override
+      @Nullable
+      public String lookupName(int id)
+      {
+        assert id == 0 : "id = " + id;
+        return null;
+      }
+
+      @Override
+      public boolean nameLookupPossibleInAdvance()
+      {
+        return true;
+      }
+
+      @Nullable
+      @Override
+      public IdLookup idLookup()
+      {
+        return this;
+      }
+
+      @Override
+      public int lookupId(@Nullable String name)
+      {
+        return NullHandling.isNullOrEquivalent(name) ? 0 : -1;
+      }
+
+      @Nullable
+      @Override
+      public Object getObject()
+      {
+        return null;
+      }
+
+      @Override
+      public Class classOfObject()
+      {
+        return Object.class;
+      }
+
+      @Override
+      public void inspectRuntimeShape(RuntimeShapeInspector inspector)
+      {
+        // nothing to inspect
+      }
+    }
+  }
 }

processing/src/main/java/org/apache/druid/segment/DimensionSelectorUtils.java

@@ -21,9 +21,7 @@ package org.apache.druid.segment;
 
 import com.google.common.base.Predicate;
 import com.google.common.base.Predicates;
-import org.apache.druid.common.config.NullHandling;
 import org.apache.druid.java.util.common.IAE;
-import org.apache.druid.query.extraction.ExtractionFn;
 import org.apache.druid.query.filter.ValueMatcher;
 import org.apache.druid.query.monomorphicprocessing.RuntimeShapeInspector;
 import org.apache.druid.segment.data.IndexedInts;
@@ -265,32 +263,4 @@ public final class DimensionSelectorUtils
     }
     return valueIds;
   }
-
-  public static DimensionSelector constantSelector(@Nullable final String value)
-  {
-    if (NullHandling.isNullOrEquivalent(value)) {
-      return NullDimensionSelector.instance();
-    } else {
-      return new ConstantDimensionSelector(value);
-    }
-  }
-
-  public static DimensionSelector constantSelector(
-      @Nullable final String value,
-      @Nullable final ExtractionFn extractionFn
-  )
-  {
-    if (extractionFn == null) {
-      return constantSelector(value);
-    } else {
-      return constantSelector(extractionFn.apply(value));
-    }
-  }
-
-  public static boolean isNilSelector(final DimensionSelector selector)
-  {
-    return selector.nameLookupPossibleInAdvance()
-           && selector.getValueCardinality() == 1
-           && selector.lookupName(0) == null;
-  }
 }

processing/src/main/java/org/apache/druid/segment/NullDimensionSelector.java

@@ -1,128 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one
- * or more contributor license agreements.  See the NOTICE file
- * distributed with this work for additional information
- * regarding copyright ownership.  The ASF licenses this file
- * to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance
- * with the License.  You may obtain a copy of the License at
- *
- *   http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-
-package org.apache.druid.segment;
-
-import com.google.common.base.Predicate;
-import org.apache.druid.common.config.NullHandling;
-import org.apache.druid.query.filter.ValueMatcher;
-import org.apache.druid.query.monomorphicprocessing.RuntimeShapeInspector;
-import org.apache.druid.segment.data.IndexedInts;
-import org.apache.druid.segment.data.ZeroIndexedInts;
-import org.apache.druid.segment.filter.BooleanValueMatcher;
-import org.apache.druid.segment.historical.SingleValueHistoricalDimensionSelector;
-
-import javax.annotation.Nullable;
-
-public class NullDimensionSelector implements SingleValueHistoricalDimensionSelector, IdLookup
-{
-  private static final NullDimensionSelector INSTANCE = new NullDimensionSelector();
-
-  private NullDimensionSelector()
-  {
-    // Singleton.
-  }
-
-  public static NullDimensionSelector instance()
-  {
-    return INSTANCE;
-  }
-
-  @Override
-  public IndexedInts getRow()
-  {
-    return ZeroIndexedInts.instance();
-  }
-
-  @Override
-  public int getRowValue(int offset)
-  {
-    return 0;
-  }
-
-  @Override
-  public IndexedInts getRow(int offset)
-  {
-    return getRow();
-  }
-
-  @Override
-  public ValueMatcher makeValueMatcher(@Nullable String value)
-  {
-    return BooleanValueMatcher.of(value == null);
-  }
-
-  @Override
-  public ValueMatcher makeValueMatcher(Predicate<String> predicate)
-  {
-    return BooleanValueMatcher.of(predicate.apply(null));
-  }
-
-  @Override
-  public int getValueCardinality()
-  {
-    return 1;
-  }
-
-  @Override
-  @Nullable
-  public String lookupName(int id)
-  {
-    assert id == 0 : "id = " + id;
-    return null;
-  }
-
-  @Override
-  public boolean nameLookupPossibleInAdvance()
-  {
-    return true;
-  }
-
-  @Nullable
-  @Override
-  public IdLookup idLookup()
-  {
-    return this;
-  }
-
-  @Override
-  public int lookupId(@Nullable String name)
-  {
-    return NullHandling.isNullOrEquivalent(name) ? 0 : -1;
-  }
-
-  @Nullable
-  @Override
-  public Object getObject()
-  {
-    return null;
-  }
-
-  @Override
-  public Class classOfObject()
-  {
-    return Object.class;
-  }
-
-  @Override
-  public void inspectRuntimeShape(RuntimeShapeInspector inspector)
-  {
-    // nothing to inspect
-  }
-}

processing/src/main/java/org/apache/druid/segment/QueryableIndexColumnSelectorFactory.java

@@ -81,7 +81,7 @@ class QueryableIndexColumnSelectorFactory implements ColumnSelectorFactory
 
     final ColumnHolder columnHolder = index.getColumnHolder(dimension);
     if (columnHolder == null) {
-      return DimensionSelectorUtils.constantSelector(null, extractionFn);
+      return DimensionSelector.constant(null, extractionFn);
     }
 
     if (dimension.equals(ColumnHolder.TIME_COLUMN_NAME)) {
@@ -108,7 +108,7 @@ class QueryableIndexColumnSelectorFactory implements ColumnSelectorFactory
       //noinspection unchecked
       return ((DictionaryEncodedColumn<String>) column).makeDimensionSelector(offset, extractionFn);
     } else {
-      return DimensionSelectorUtils.constantSelector(null, extractionFn);
+      return DimensionSelector.constant(null, extractionFn);
     }
   }
 

processing/src/main/java/org/apache/druid/segment/incremental/IncrementalIndexColumnSelectorFactory.java

@@ -25,7 +25,6 @@ import org.apache.druid.segment.ColumnSelectorFactory;
 import org.apache.druid.segment.ColumnValueSelector;
 import org.apache.druid.segment.DimensionIndexer;
 import org.apache.druid.segment.DimensionSelector;
-import org.apache.druid.segment.DimensionSelectorUtils;
 import org.apache.druid.segment.SingleScanTimeDimensionSelector;
 import org.apache.druid.segment.VirtualColumns;
 import org.apache.druid.segment.column.ColumnCapabilities;
@@ -81,7 +80,7 @@ class IncrementalIndexColumnSelectorFactory implements ColumnSelectorFactory
       // not a dimension, column may be a metric
       ColumnCapabilities capabilities = getColumnCapabilities(dimension);
       if (capabilities == null) {
-        return DimensionSelectorUtils.constantSelector(null, extractionFn);
+        return DimensionSelector.constant(null, extractionFn);
       }
       if (capabilities.getType().isNumeric()) {
         return capabilities.getType().makeNumericWrappingDimensionSelector(
@@ -91,7 +90,7 @@ class IncrementalIndexColumnSelectorFactory implements ColumnSelectorFactory
       }
 
       // if we can't wrap the base column, just return a column of all nulls
-      return DimensionSelectorUtils.constantSelector(null, extractionFn);
+      return DimensionSelector.constant(null, extractionFn);
     } else {
       final DimensionIndexer indexer = dimensionDesc.getIndexer();
       return indexer.makeDimensionSelector(dimensionSpec, rowHolder, dimensionDesc);

processing/src/main/java/org/apache/druid/segment/virtual/ExpressionSelectors.java

@@ -37,9 +37,7 @@ import org.apache.druid.segment.ColumnSelectorFactory;
 import org.apache.druid.segment.ColumnValueSelector;
 import org.apache.druid.segment.ConstantExprEvalSelector;
 import org.apache.druid.segment.DimensionSelector;
-import org.apache.druid.segment.DimensionSelectorUtils;
 import org.apache.druid.segment.NilColumnValueSelector;
-import org.apache.druid.segment.NullDimensionSelector;
 import org.apache.druid.segment.column.ColumnCapabilities;
 import org.apache.druid.segment.column.ColumnHolder;
 import org.apache.druid.segment.column.ValueType;
@@ -195,10 +193,10 @@ public class ExpressionSelectors
 
     if (baseSelector instanceof ConstantExprEvalSelector) {
       // Optimization for dimension selectors on constants.
-      return DimensionSelectorUtils.constantSelector(baseSelector.getObject().asString(), extractionFn);
+      return DimensionSelector.constant(baseSelector.getObject().asString(), extractionFn);
     } else if (baseSelector instanceof NilColumnValueSelector) {
       // Optimization for null dimension selector.
-      return NullDimensionSelector.instance();
+      return DimensionSelector.constant(null);
     } else if (extractionFn == null) {
       class DefaultExpressionDimensionSelector extends BaseSingleValueDimensionSelector
       {

processing/src/test/java/org/apache/druid/segment/ConstantDimensionSelectorTest.java

@@ -28,13 +28,13 @@ import org.junit.Test;
 
 public class ConstantDimensionSelectorTest
 {
-  private final DimensionSelector NULL_SELECTOR = DimensionSelectorUtils.constantSelector(null);
+  private final DimensionSelector NULL_SELECTOR = DimensionSelector.constant(null);
-  private final DimensionSelector CONST_SELECTOR = DimensionSelectorUtils.constantSelector("billy");
+  private final DimensionSelector CONST_SELECTOR = DimensionSelector.constant("billy");
-  private final DimensionSelector NULL_EXTRACTION_SELECTOR = DimensionSelectorUtils.constantSelector(
+  private final DimensionSelector NULL_EXTRACTION_SELECTOR = DimensionSelector.constant(
       null,
       new StringFormatExtractionFn("billy")
   );
-  private final DimensionSelector CONST_EXTRACTION_SELECTOR = DimensionSelectorUtils.constantSelector(
+  private final DimensionSelector CONST_EXTRACTION_SELECTOR = DimensionSelector.constant(
       "billybilly",
       new SubstringDimExtractionFn(0, 5)
   );